U.S. Pat. No. 4,427,878 to Buchtel et al. describes an optical scanning apparatus for a gyroscopic missile seeker. FIG. 2 of that patent shows the counter-rotating traction drive for the optics of that apparatus. In that drive, balls driven by an outer race rotate in a fixed keeper or retainer having arcreate separator portions so as to drive an inner race in the opposite direction and at a higher speed.
In practice, the parts involved in a traction drive assembly of this type are very small; the entire assembly is typically less than 1 cm in diameter. Although the retainer is made of porous, lubricant-impregnated bronze, the forces generated at the rotational speeds and loads involved are great enough to rapidly wear and smear the bronze surface of the retainer where the drive balls rub against it. As a result, the retainer becomes incapable of providing sufficient lubrication at the contact surface, and thereby appreciably shortening the life of the assembly.